1. Field of the Invention
This invention relates generally to superabrasive cutting elements and, more specifically, to polycrystalline diamond compact cutting elements comprising a polycrystalline diamond table formed and bonded to a supporting substrate or backing during formation of the cutting element and drill bits for subterranean drilling equipped with such cutting elements.
2. State of the Art
Superabrasive elements are used extensively in drilling, cutting, milling, and other operations relating to the removal of portions of hard materials. A superabrasive element useful in subterranean, drilling may conventionally include a table formed of polycrystalline diamond particles or, less typically, cubic boron nitride particles sintered under high pressure, high temperature conditions into a coherent conglomerate mass termed a "compact." In order to support the hard but relatively brittle table, it is typically bonded during sintering to a substrate of, e.g., cemented carbide. A plurality of such cutting elements is typically mounted to a rotary drill bit for drilling subterranean formations.
Typically, such cutting elements are formed by placing a cemented tungsten carbide substrate preform into a press, and placing, for example, diamond grains, optionally with a catalyst binder, atop the substrate preform. Under the aforementioned high pressure and temperature, the diamond grains are bonded to each other and to the substrate in the sintering process, forming a diamond table.
Polycrystalline diamond compact cutting elements, commonly known as PDCs, have been commercially available for more than 20 years and have been widely used, particularly on bits for subterranean drilling. In a variation of the PDC, residual metal and catalyst is leached from the diamond table to form a thermally stable product (TSP), or a silicon-bonded TSP may be formed, silicon having a coefficient of thermal expansion (CTE) similar to that of diamond.
The use of PDC and TSP cutting elements in rotary drag bits for earth boring has resulted in major increases in penetration rates and overall reductions in drilling costs for a broadened range of rock formation types.
Nevertheless, several problems have become evident in using PDC and TSP cutting elements. High residual stresses attributable to the aforementioned high pressure, high temperature fabrication conditions may be present in such cutting elements, particularly adjacent the table-substrate interface, and may lead to fracturing of the superabrasive table, separation from the substrate and failure of the element. Such stresses are largely attributable to the differences in CTE between the diamond and the carbide; cooling of the cutting element after fabrication results in greater shrinkage of the substrate than of the polycrystalline diamond material.
Furthermore, spalling, fracture and delamination of the table material from the substrate may occur during attachment of the cutting element to a tool, or during normal drilling operations, because of high bending forces applied during attachment, or by contact with the subterranean formation itself as weight on bit (WOB) is applied and torque is applied to rotate the bit to engage the formation. Diamond has an extremely low strain rate to failure and cannot tolerate flexing resulting from high applied forces. Fracture or delamination, once initiated, ultimately leads to failure of the cutting element. Any means to reduce the frequency of bit failure will have a significant beneficial economic effect in drilling operations.
Various attempts have been made to reduce the incidence of cutting element failures adjacent the table/substrate interface.
In U.S. Pat. No. 4,629,373 of Hall, the substrate is eliminated, and the cutting table is directly attached to, e.g., a metal drill bit. The attachment surface is formed with surface irregularities including parallel grooves, crosshatch grooves, wire-mesh grooves, and the like.
The disclosure of Griffin in U.S. Pat. No. 5,469,927 teaches the addition of a transition layer between the cutting table and the substrate, in which the transition layer has at least one property intermediate the properties of the cutting table and the substrate. In U.S. Pat. No. 5,011,515 of Frushour, a transition layer has properties which gradually vary from the cutting table to the substrate.
The substrate-table interface may be formed with a series of sloping surfaces about a central axis, as depicted in U.S. Pat. Nos. 5,484,330 and 5,486,137 of Flood et al.
In U.S. Pat. No. 5,709,279 of Dennis, the table-substrate interface is formed in an undulating sinusoidal wave fonn, the sine wave amplitude varying in a direction parallel to the central axis.
As taught in U.S. Pat. No. 5,605,199 of Newton, the cutting table may be formed with increased thickness about its periphery. In addition, a series of adjacent, parallel, straight grooves and ridges in the interface is shown.
In U.S. Pat. No. 5,564,511 of Frushour and U.S. Pat. No. 5,622,233 of Griffin, the table/substrate interface is proposed to be formed with a plurality of-discrete protuberances projecting perpendicularly to the general interfacial plane. The protuberances may be bulbous or conical, the interface resembling an egg carton or acoustical foam.
In U.S. Pat. No. 5,007,207 of Phaal and U.S. Pat. No. 5,355,969 of Hardy et al., concentric circular or semicircular ridges and grooves about a central axis of the interface are shown.
In U.S. Pat. No. of 5,351,772 of Smith, a wide variety of interfacial patterns is shown with radially directed, interleaved grooves and ridges.
In U.S. Pat. No. 5,590,728 of Matthias et al., table-substrate interfaces are shown with generally radially directed grooves and ridges having straight, angular, bulbous, or somewhat twisted configurations.
In U.S. Pat. No. 5,611,649 of Matthias, a star-shaped pattern of interfacial grooves and ridges is shown. Both U.S. Pat. No. 5,611,649 of Matthias and U.S. Pat. No. 5,617,928 of Matthias et al. teach the use of concentric semicircular grooves and ridges with a central axis outside or nearly outside the circumferential periphery of the table and substrate.
Despite all the aforementioned suggested improvements in the interface design, cutting elements continue to fail because of high loads and attendant stresses experienced during drilling operations. Drill bit repair and replacement and consequent lost rig time comprise major expenses in the drilling industry. Thus, further advancements in the art are necessary to enhance the cutting table-substrate bond strength in order to improve drill bit performance reduce downtime and the necessity for cutting element replacement and drill bit replacement and repair.